David Fassler, a psychiatrist who testified at the hearing on behalf of the American Psychiatric Association, said in an interview, "Hearings like this frighten parents and make it less likely they will bring their kids in for treatment."

Fassler and other leaders in American psychiatry say large numbers of depressed children are untreated. "Medications can be lifesaving, but medications alone are not the answer," he said.

Increasingly, however, American doctors have come to rely on drugs. Officials said yesterday that 2.1 million prescriptions for antidepressants were written for children in 2002.

A key problem, both critics and advocates said, is that the clinical trials conducted by drug companies were not designed to answer the questions that are being raised. FDA officials are trying to make comparisons among studies that used different terms to describe suicidal tendencies and different measures of what constitutes a suicidal thought or attempt.

While FDA investigators had found that "these drugs are associated with a risk of suicidal behavior in children," said Russell Katz, director of FDA's neuropharmacology division, "we are concerned that the categorization of events is not entirely reliable."

Thomas Laughren, team leader of FDA's psychiatric drug products group, wrote in a briefing paper that "there are signals of increased risk of events suggestive of suicidality for several of these drugs" but that the data were confusing. Not all trials showed such a connection, and companies used different measures to classify and count cases.

"Is there a causal link between antidepressants and suicidality?" he asked yesterday. "To err in either direction has adverse consequences."

Researchers at Columbia will study narrative reports of adverse effects and reclassify them according to uniform criteria. The FDA asked nine drugmakers to submit details of every adverse report suffered by about 4,000 children across 25 trials. The Columbia group will not be told in advance how the companies classified the cases.

In all the trials, children with similar levels of depression were randomly chosen to receive either drugs or dummy pills. Laughren said there were 109 who were reported to have made at least one suicide attempt or had suicidal thoughts after taking a drug. The companies, however, screened out children who were suicidal to begin with, making the results of the studies less applicable to the real world, where doctors often use the medicines to treat suicidal children.

Of the 109 children, Laughren said, 66 harmed themselves. Among them, 19 cut themselves and 37 took overdoses of pills. Two children tried to hang themselves, and there was one case of self-burning -- these last three suicide attempts were halted by alert caregivers. Forty-seven were hospitalized, but none committed suicide.

David Healy, a Welsh psychiatrist who has campaigned for more careful use of the medicines, estimated that about 500 American children have committed suicide as a result of antidepressants. Irving Kirsch, another critic, said the vast majority of clinical trials had failed to show that the drugs made patients any better than did dummy pills. Even when the medicines worked, he estimated that 87 percent of the benefit derived from the patients' belief that they were effective, a phenomenon known as the placebo effect.